Nearly half of the detainees remaining at Guantanamo Bay are slated for transfer, a Pentagon official confirmed to Fox News.

Of the 76 remaining detainees, 34 have been approved for transfer to countries that have agreed to accept them, according to spokeswoman Valerie Henderson.

Thirty-two other detainees are slated to have their cases heard by a Department of Defense review board.

Not all the detainees that get transferred to other countries will go to prison, however, and the details of the terms of each transfer with other nations remain a secret.

Ten other detainees at Gitmo cannot be transferred based on the severity of the charges they face.

The developments continue to fuel concerns among critics that some of these detainees could return to terror. They cite statistics from the Director of National Intelligence that say nearly 30 percent of those who have been released have returned to the battlefield or have been suspected of doing so.

While President Obama has called those transferred to date “low level individuals,” defense officials with knowledge of the recent transfers and of those remaining at the detention center call these men the “worst of the worst.”

Some of the detainees approved for transfer out of Gitmo were involved in the 9/11 attacks, according to Thomas Joscelyn, a senior fellow at the Foundation for Defense of Democracies.

Earlier this year, a detainee transferred to Uruguay in 2014 went missing. It is rumored that Jihad Ahmed Mustafa Dhiab, an Al Qaeda operative, traveled to Syria to rejoin his old cohorts, but other officials are concerned the Syrian national may still be in South America and could be plotting an attack in Brazil during the Olympics.

In recent months, Republicans on Capitol Hill have put forth legislation to prevent the transfer of the remaining detainees.

The Miami Herald first reported the new Gitmo numbers, though the Pentagon’s numbers differ slightly by one detainee.

Lucas Tomlinson is the Pentagon and State Department producer for Fox News Channel. You can follow him on Twitter: @LucasFoxNews